The present invention relates to a fuel injector.
Fuel injectors having a component part for guiding a valve needle described in German Patent Application No. DE 36 43 523. They include a swirl disk disposed upstream from the valve-sealing seat, which has a central guide bore. Swirl channels, connecting the fuel-pressurized chamber, which is located upstream from the swirl disk, to a swirl chamber adjoining in the flow direction, guide the flow. When the valve is open, the fuel flows from the swirl channels into the swirl chamber, the velocity vector having a component in the circumferential direction. The central bore of the swirl disk guides the valve-closure member, or the valve needle. The swirl disk concentrically adjusts itself by a conical seat surface in the area of the valve seat, where it is sealingly held due to the throttling of the fuel flow. To prevent a secondary flow path for the fuel along the guide bore, the opening in the swirl disk is narrowly toleranced in relation to the valve needle and the valve-closure member.
Moreover, German Patent Application No. DE 196 25 059 describes a fuel injector where the guide of the valve needle, or the valve-closure member, is disposed in a subassembly upstream from the valve seat. As in DE 36 43 523, a secondary flow path is prevented by a small gap dimension between the guide bore and valve needle, or valve-closure member. A swirl is generated by bores, which have a tangential component and discharge upstream from the valve-sealing seat. The valve needle is guided in a sleeve which, in turn, is centered in the valve seat by a downstream conical form. In a further exemplary embodiment, the valve-seat member and the guide are designed as one piece.
Disadvantageous in these fuel injectors is the high degree of precision required in the manufacture of the valve""s component parts. The swirl formation is highly dependent on the flow-through of the swirl channels. If a secondary flow path is present for the fuel, this will result in a flow portion lacking circumferential speed, which negatively affects the swirl generation and, consequently, the fuel atomization. In the final analysis, the combustion will be less efficient. Due to the manufacturing process, the dimensions of the component parts are tolerance-encumbered. This may cause an angle error of the valve needle, or the valve-closure member, in the area of the valve-seat. In the afore-mentioned fuel injectors, the valve needle, or the valve-closure member, is guided by a component part which is centered in the nozzle body either in a form-locking or force-locking manner. Thus, the orientation of the guide bore relative to the position of the valve needle, or the valve-closure member, cannot be adjusted. It is only possible to compensate for the positional deviation by enlarging the guide bore. This also enlarges the secondary flow path, which will change the metered fuel quantity and the spray-off pattern. Expensive production methods are used to meet the high demands of a precise spray-off pattern and the metered fuel quantity, in this way ensuring an exact finishing and installation of all relevant component parts with respect to their position relative to the center axis of the fuel injector.
A fuel injector according to the present invention may have the advantage over that the center axis of the valve needle may be inclined relative to the center axis of the fuel injector, without this requiring a modification of the fit between the valve needle, or valve-seat member, and the guiding bore. The use of two component parts, which are flexibly supported inside each other, makes it possible to incline a guide compensator together with the valve needle. The guide compensator and the valve needle remain in correct positional alignment, thereby improving the sealing fit between both component parts. The angle compensation between the valve needle and the center axis of the fuel injector is achieved by a sealing seat being formed between the guide compensator and a swirl disk, the sealing seat being flexible with respect to the angle between the center axes of the swirl disk and the guide compensator. As a result, the entire fuel flow reaching the spray-off orifice flows through the swirl channels, allowing a defined swirl generation and precise metering of a fuel quantity to be sprayed off.
It is advantageous in this context that the swirl disk may be manufactured together with the guide compensator and a spring as a sub-assembly. In the further installation process, the entire subassembly can then be treated as a single component.
Also advantageous is the common center point of the spherical sealing surface of the guide compensator and the spherical valve-closure member in the rest state of the fuel injector. The position of the valve-closure member is clearly defined by the valve-seat member. An angle error, therefore, will merely result in a rotation about the center point of the spherical valve-closure member. A rotation about the common center point will not affect the sealing contact of both sealing seats.